High spatial resolution inorganic scintillator detector for high‐energy X‐ray beam at small field irradiation

Abstract

Purpose Small field dosimetry for radiotherapy is one of the major challenges due to the size of most dosimeters, for example, sufficient spatial resolution, accurate dose distribution and energy dependency of the detector. In this context, the purpose of this research is to develop a small size scintillating detector targeting small field dosimetry and compare its performance with other commercial detectors. Method An inorganic scintillator detector (ISD) of about 200 µm outer diameter was developed and tested through different small field dosimetric characterizations under high‐energy photons (6 and 15 MV) delivered by an Elekta Linear Accelerator (LINAC). Percentage depth dose (PDD) and beam profile measurements were compared using dosimeters from PTW namely, microdiamond and PinPoint three‐dimensional (PP3D) detector. A background fiber method has been considered to quantitate and eliminate the minimal Cerenkov effect from the total optical signal magnitude. Measurements were performed inside a water phantom under IAEA Technical Reports Series recommendations (IAEA TRS 381 and TRS 483). Results Small fields ranging from 3 × 3 cm2, down to 0.5 × 0.5 cm2 were sequentially measured using the ISD and commercial dosimeters, and a good agreement was obtained among all measurements. The result also shows that, scintillating detector has good repeatability and reproducibility of the output signal with maximum deviation of 0.26% and 0.5% respectively. The Full Width Half Maximum (FWHM) was measured 0.55 cm for the smallest available square size field of 0.5 × 0.5 cm2, where the discrepancy of 0.05 cm is due to the scattering effects inside the water and convolution effect between field and detector geometries. Percentage depth dose factor dependence variation with water depth exhibits nearly the same behavior for all tested detectors. The ISD allows to perform dose measurements at a very high accuracy from low (50 cGy/min) to high dose rates (800 cGy/min) and was found to be independent of dose rate variation. The detection system also showed an excellent linearity with dose; hence, calibration was easily achieved. Conclusions The developed detector can be used to accurately measure the delivered dose at small fields during the treatment of small volume tumors. The author's measurement shows that despite using a nonwater‐equivalent detector, the detector can be a powerful candidate for beam characterization and quality assurance in, for example, radiosurgery, Intensity‐Modulated Radiotherapy (IMRT), and brachytherapy. Our detector can provide real‐time dose measurement and good spatial resolution with immediate readout, simplicity, flexibility, and robustness.

High resolution small‐scale inorganic scintillator detector: HDR brachytherapy application

“…FG050UGA) was provided by Thorlabs ™ . According to the technique, already detailed in, 20 fiber clipping, apex testing, grafting technique (PMMA resist diluted in Ethyl lactate (C 5 H 10 O 3 ) solvent used), and fabrication of the ISD was studied to develop the fiber integrated inorganic detector. After fabricating the ISD with (Zn,Cd)S:Ag scintillating materials, the estimated scintillating volume of the detector is 2.9 × 10 −9 cm 3 .…”

“…32,33 Note that, this signal is expected to be insignificant due to the small size silica fiber volume irradiated, and as characterized previously. 20 However, a bare fiber was used to quantify the stem signal, so that the exact ISD output signal can be ensured. Thus, the exact scintillation signal generated due to the irradiation is measured by subtracting stem signal and the dark noise from the total signal.…”

“…Due to very low signal attenuation (30 dB/ km) through the optical fiber, the system does not require any corrections for signal transmission loss throughout the fiber. 20…”

“…Fiber based scintillating dosimetry system that consists of scintillating materials coupled to the optical fiber apex has already been used in different high energy radiation measurements. [20][21][22][23] The scintillator-based detector was proposed by several research groups and can be useful to measure the step dose gradient nearby the tumor in the case of BT treatment 15,[24][25][26] Scintillators used in those dosimeters can be organic or inorganic. These reduced size detectors can mitigate the issue of volume averaging effect and can facilitate the accurate dose measurement in the tumor region and identify the treatment error.…”

“…14,[24][25][26] Despite the aforementioned advantages, the major issue of using these scintillating detectors is stem effect, induced in the fiber, a combination of Cerenkov and fiber excited luminescence when large core plastic fiber is irradiated. 20,22,28,29 This effect is also related to the exposed volume of the detector, and fiber used in the detector. Indeed, conventional detectors require a significant volume of scintillators and optical fiber cable to detect and transmit the scintillating signal.…”